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E- -Ell MM1M-- r' Page 6 July 12, 1991 Y Joh No,400511-1:1 or grout to the toll of the clay layer. "fho ntonitaring well will he completed in the portion of the saturated zone overlying the clay layer. The monitoring wells will he constructed 0f2-inch diameter flush-threaded,Schedule 44 PVC well casing and screen. Well screen with a slot size of 0.02-inc:t will he utilized in the well construction and the annular space surrounding the well,Screen will he backfilled to approximately 2 feet above the top of the screened section using L,onestar No. 2/12 sand. Figure 4,Proposed Monitar ing Well Detail,providesadditionaI information on the construction of the proposed ground-water monitoring wells. • Drill, log, and install nineteen (19) vapor wells at the locations shown on Figure 3. Complete the borings as 2-inch diameter wells. 'ilte wells will be ;jstalled as six (6) f clusters of three(3)with each well cluster having wells to approximate depths of 90 feet, 65 feet,and 40 feet below grade. One additional shallow vapor well will be installed next to RW-25 with an approximate depth of 40 feet. Figure 5, Proposed Vapor Well Detail, provides additional information on the construction of the proposed vapor wells. Screened intervals for the wells will be determined by the field geologist based on the s#ratigraphy of the subsurface. The deepest Wel!in each 3-well cluster shall be drilled first to establish the stragigraphy and the screen intervals for all wells to that cluster. E Develop the proposed monitoring wells and measure the depths to ground Witter and apparent free product, if any, in :tll of the wells present at the site. • Survey the elevations and locations of the newly installed wells. The well elevations will he surveyed relative to Mean Sea Level. F = i r Collect ground-water samples from each monitoring well at the site which does not contain a measurable thickness of free-float'snz.product. These ground-water samples will be analyzed for total petroleum hydrocarbons as gasoline(TPI-1g),benzene,ethylbenzene, toluene,and xylenea. • Once the wells are installed,DERS will pipe the vapor extraction wells to the equipment area and manifold the well headers. Construction of the manifold will allow each vapor well to be used as either an extraction well, or an induction well. Upon receiving the necessary air permit modification approval,the wells will he incorporated into the existing vapor extraction system(VES). . �+ DU PONT ENVIKO\htENTAL 12t.-,tE[)tA1ION SE.RVIt LS